<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <title></title>
  <script src="http://libs.baidu.com/jquery/1.10.2/jquery.min.js"></script>
  <script type="text/javascript">
    var countdown = 60;

    function settime(obj) {
      if (countdown == 0) {
        obj.removeAttribute("disabled");
        obj.value = "免费获取验证码";
        countdown = 60;
        return;
      } else {
        obj.setAttribute("disabled", true);
        obj.value = "重新发送(" + countdown + ")";
        countdown--;
      }
      setTimeout(function () {
        settime(obj)
      }, 1000)
    }
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</head>

<body>
  <input type="button" id="btn" value="免费获取验证码" onclick="settime(this)" />
</body>

</html>